Lapping apparatus



March 26, 1940. A, AL 2,195,063

LAPPING APPARATUS Original Filed July 22, 1936 2 as /00 /0a In; so?

INVENTOR fizz Z14 6! jd allace.

' A TTORNE Y Patented Mar. 26, 1940 PATENT OFFICE LAPPIN G APPARATUS David A. Wallace, Detroit, Mich., assignor to Chrysler Corporation, Highland Park, Mlch., a corporation of Delaware Original application July 22, 1936, Serial No. 91,851. Divided and this application July 1, 1938, Serial No. 216,857

4 Claims.

This invention relates to improved apparatus for lapping surfaces and is a division of my application, Serial No. 91,851, filed July 22, 1936.

More particularly the invention pertains to 5 lapping of surfaces of apparatus and parts thereof which operate in rubbing, sliding or rotative bearing-like, or frictional contact with other parts.

Heretofore, in polishing, lapping or otherwise finishing surfaces, it has been the practice to produce relative movement, mainly in one direction only, between the surfaces of the work and the lapping means. In some instances combinations of different directional movements have been employed in an effort to avoid scoring of the surface operated upon by repeated action of isolated hard particles of the lapping elementon substantially the same areas of the work. The relative movement in one direction has, however, been of a relatively low order of velocity as compared to the relative movement in another direction, and consequently, the scratch lines, scores, or inscriptions traced on the work by isolated hard particles in the lapping surface have not been or disturbed and cross-hatched as to provide finished surfaces of actual mirror-like smoothness directly by lapping operations.

Polishing with extremely fine abrasives, such as rouge, has been required after the lapping operation, to produce the desired degree of smoothness and finish. In this connection it should be noted that while polishing of this character improves the appearance of the surfaces it'does not materially change its physical smoothness. That this is true can readily be seen by microscopic observation of conventionally lapped and polished surfaces by which it is found that the multiplicity of minute ridges between adjacent scratch lines or scores are not actually re- 4 moved. The polishing compound merely forms a luster on the sides of such ridges which give the final surface, an appearance of much greater smoothness than actually exists.

Ifhave found that by producing relative movements of respectively different ranges of speed and in different directions, preferably at right angles, between the surface operated upon and the lapping surface, actual smoothness is directly obtained by lapping and such smoothness is of a much'diflerent and superior kind, than that resulting from conventional lapping followed by polishing operations. I 1 v 1 Another object ofthe'invention is to provide improved lapping apparatus by whichiphysically smooth and mirror-like surfaces can be directly apparatus of this character by which the inscriptions traced on the surface operated upon by localized hard particles in the lapping surface can be brought to a desired angular cross-hatched relationship such that the resulting scratch lines are accordingly so repeatedly cross-hatched as to destroy their normal roughness producing effect. I

An additional object of the invention is to provide apparatus of this character by which the reciprocating movement of the lapping element is maintained at a sufficiently high velocity and frequency to produce smooth surfaces free from grooves and scores with a limited amount of reciprocatory movement.

A still further object of the invention is to provide apparatus of this character by which a lapping element can be conveniently reciprocated, during application thereof to a rotating piece of work, at a relatively high rate of speed of a vibratory order.

A still further object of the invention is to provide an improved lapping device which will operate a plurality of conveniently attachable and detachable lapping elements so as to facilitate adaptation of the device to the lapping of a plurality of different types of pieces of work.

Another object of the invention is to provide lapping apparatus of this character by which the relative movement between the lapping ele-. ment and the work in one direction is of a reciprocatory nature and which movement varies in velocity from zero at opposite ends'of the stroke while maintaining a substantially high velocity through out the main portion of the stroke.

Other objects of the invention are to provide improved lapping element holders by which a plurality'of lapping surfaces can be held against the work with substantially uniform pressure; to

provide an improved lapping device by which the inner surfaces of annular members such as brake drums and cylinders can be lapped in accordance with the invention.

Illustrative embodiments of the invention are shown in the accompanying drawing, in which: i

Fig. 2 is a fragmentary transverse vertical sectional view taken on the line 2-2 of Fig. 1.

In the form of the invention illustrated in the drawing, both the rotative movement of the work and the reciprocatory movement of the lapping elements operating thereon are produced by suitable driving means. In this form of the invention the lapping apparatus comprises a stationary casing 10 provided with spaced bearings 80 in which a tubular shaft 8| is journalled. Mounted on the tubular shaft 8| is a worm wheel 82 which is driven by a worm 83 operatively connected, in turn, to a prime mover such as an electric motor or other suitable driving mechanism. The shaft 8| has a bevel gear 84 non-rotatively fixed thereto which is meshed with bevel pinion teeth 85 formed on the inner end of a stub shaft 86. The stub shaft 86 is journalled in a bearing 81 mounted in the wall of the casing I and has an external end provided with an eccentric pin 88.

. Slidably mounted in a channel 89 formed on the exterior of.the casing I0 is a slide block 90 on which a lapping element holder, generally designated by the numeral 9|, is mounted. The slide block 90 has a recess in its lower side for receiving the eccentric pin 88 and by the agency of which the block 90 is reciprocated. v

A shaft 92 extends axially through the tubular shaft 8| and is supported at its left end, as revealed in Fig. 1, by a dead spindle 93, the right end of the shaft 92 being supported by and operatively connected with a live spindle 94 by which it is rotated. Provided on the left end portion of the shaft 92 are a pair of coupling members 95 and 96 for non-rotatably attaching to the shaft 92 an article, such for example as a vehicle wheel brake drum 9'! which has any internal cylindrical surface 98 to be'lapped. The article to be operated upon may be secured to the shaft 92 in any desired manner, the form of attachment shown in the drawing being merely for illustrative purposes. In this case, the brake drum is detachably and drivingly secured to the shaft 92 by axial pressure of the coupling element 95 on a hub part 99 on which the drum 9'! is mounted, such axial pressure being resisted by a thrust ring I00 which bears against the coupling element 96.

The lapping element holder 9| comprises a flexible and resilient backing element I00, preferably formed of resilient sheet metal, on one side of which are mounted a plurality of sockets IOI in each of which is disposed a lapping element I02. The lapping elements may comprise a stone structure or any other polishing material. The intermediate portion 6f the lapping element holder 9| is yieldably urged outwardly to press the lapping elements into operative engagement with the surface 98- of the drum by a pair of coil springs I03, each of which is located in a slot I04 formed in the slide block 90 and which bear between the bottom of the slot I04 and the lower side of the flexible backing'strip I00. The lapping elementholder is held against excessive outward movement by the springs I03 by a stem I05 which extends through the wall of the casing I0 and which is provided with the head I06 having an elongated slot I01 formed therein. The head I00 is received between a pair of aper-- ture lugs' I08 carried by the flexible backing I00 and it is movably attached to the lugs I08 by a pin H0, as illustrated in Fig. 2. Provided on the lower end of the stem I05 is a nut III which is adapted to engage an abutment II2 to prevent excessive outward movement of the lapping element holder. The pin and slot connection between the stem I05 and the lapping element holder accommodates reciprocatory movement of the latter during operation of the device. It is to be understood that in this form of the invention the relative velocity of reciprocatory and rotative movements of the lapping elements and brake drum, respectively, are predetermined in the following manner.

In order to assure the application of uniform pressure upon the surface 98 by all the lapping elements I02, it is preferable to so form the resilient yieldable backing I00 of the holder that when it is in its relaxed state, it will have a greater radius of curvature or less actual curvature than the surface with which it is intended to bring the lapping elements into conformity. Thus, when pressure is applied at the intermediate portion of the backing I00 all lapping elements are applied to the surface operated upon at substantially uniform pressure.-

During operation of the foregoing apparatus the work is rotated continuously 'in one direction and the lapping elements are reciprocated in a direction substantially parallel to the axis of IO- tation of the work. The linear velocity of these respective different directional movements are so predetermined as to bring the resultants of the movements during successive half cycles of the reciprocatory movement into predetermined angular relationship with respect to each other. I

It is preferable to cause the resultants of the movements produced during successive half cycles of the reciprocatory movement to intersect at substantially right angles of each other. To accomplish this, the linear velocity of the surface operated upon and the-linear velocity of the lapping elements must be substantially equal. However, since the velocity of the reciprocatory movement varies, this condition is not maintained at all times but is approached throughout the main portions of the strokes of the lapping elements. Localized hard areas of the lapping surface, therefore, trace inscriptions on the surface of the work during successive half cycles of the reciprocatory movement which are cross-hatched at a plurality of different angles forming an heterogeneous arrangement of cross-hatched scratch lines, none of which develop into deep grooves or scores. While it is preferable to so predetermine the linear velocity of the movement of the work and movement of the lapping elements as to bring the main portions of the scratch lines to approach right angle'relationship with respect to each other, it is foundthatexcellent results are obtained when the angularity of the lines traced during successive half cycles of the reciprocatory'movement is such that the minimum angle therebetween is substantially forty degrees. In other words, the resultant of'the two directional movements may vary from an inclination of substantially twenty to substantially seventy degrees to the path of reciprocatory movement. For the purpose of illustration, a cylindrical surface of substantially three and oneeighth inches in diameter would be rotated at approximately sixty R. P.'M'. and the lapping turning or other machining of the surfaces are 76 smoothness in a relatively short time and without danger of removing sufficient material to render the articles undersize. The smoothness resulting from the actual removal of the ridges without introducing other ridges by application of the lapping elements to the surface, is of much superior order than the mere lustrous finish resulting from polishing the side surfaces of the ridges. The large number of strokes of the lapping elements across the ridges in a direction substantially normal to their lengths, resulting from reciprocation of the lapping elements at a rate of a vibratory order, assures removal of the ridges and not mere polishing or partial flattening thereof.

Although but one specific embodiment of the invention has been herein shown and described, it is understood that various changes of details of construction and operation may be made without departing from the spirit and scope of the invention.

What I claim is:

\1. Lapping apparatus including means for rotatably supporting an article having a recess and anassociated internal cylindrical surface, driving means for rotating said article, a stationary support insertable into said recess, a 'reciprocable lapping element slidably mounted on said support and engageable with said surface throughout a major portion of its axial dimension, said lapping element comprising a flexible base portion conforming to the curvature of said surface and a plurality of circumferentially spaced abrading stones, and means on said support for independently drivingly reciprocating said lapping element during rotation of said article, said means being so constructed and arranged as to impart to said lapping element a linear abrading reciprocating movement of a short stroke of substantially less length than the length of contact between said surface and said lapping-element and of substantially the same order of velocity as the velocity of the linear movement of said surface.

2. Finishing apparatus including means for rotatably supporting a piece of work having an opening therein surrounded by a curvilinear surface, means for drivingly rotating said work, a support insertable into said opening, anabrading tool reciprocably mounted on said support comprising a base portion and a resiliently deformable head conformable to thecurvature of said surface and having a plurality of spaced abrading stones thereon engageable with said surface, and means on said support for drivingly reciprocating said tool throughout a short stroke comprising only a small fractional part of the axial dimension of said surface during rotation of said work, said means being so constructed and arranged as to impart to said tool a linear movement of substantially the same order of velocity as the velocity of the linear movement of said surface and resilient .means acting upon said deformable head at the central portion thereof for urging said stones against said surface.

3. Apparatus for finishing a piece of work having an opening therein surrounded by an internal surface portion to be finished including relatively rotatable support members for said work and for a finishing tool respectively, said tool support member being insertable into said opening, said tool comprising a flexible head reciprocably mounted on said tool support member and having a plurality of circumferentially arranged abrading elements engageable with said surface, means for urging said abrading elements against said surface, guide members on said tool support for confiningthe reciprocatory movement of said tool to a course in the direction of the axis of said relative rotation, means for drivingly producing relative rotation of said work and tool support members, and means for drivingly reciprocating said tool relative to said tool support member during relative rotation of the latter and said work.

4. Apparatus for lapping a piece of Work having an opening .therein bounded by an internal surface portion to be lapped including relatively rotatable support members for said work and for a lapping tool respectively, said lapping element support member being insertable in said opening, a lapping tool comprising a base portion reciprocably mounted onsaid lapping tool support member and a resiliently yieldable head portion having a plurality of lapping elements thereon engageable with said surface, means acting between said tool and said tool support member including resilient members for urging the latter toward said surface, guide members on said tool support member for confining the reciprocatory movement of said tool to a course in the direction of the axis of said relative rotation, mechanism for drivingly producing relative rotation of said work and tool support members, and means for drivingly reciprocating said tool relative to said tool support member during said relative rotation of the latter and said work support member.

DAVID A. WALLACE. 

